1. Field of the Invention
The present invention concerns a rotary bending and forming device, and more particularly, an extended length rotary bending and forming device and method for manufacture thereof.
2. Description of the Related Art
Rotary bending devices of the type with which the present invention is generally concerned are well known, for example, from U.S. Pat. No. 5,404,742 to Wilson entitled "Rotary hemming device"; U.S. Pat. No. 4,756,863 to Petershofer entitled "Method for hot-forming a laminated sheet of synthetic resin and a device for working this method"; U.S. Pat. No. 5,253,502 to Poletti entitled "Apparatus and method for bending and forming sheet material"; U.S. Pat. No. 5,462,424 to Kuroyone entitled "Metallic die device for press machine"; U.S. Pat. No. 5,474,437 to Kuroyone entitled "Metallic die device for press machine"; U.S. Pat. No. 4,092,840 to Eckold entitled "Device for flanging the edges of sheet sections"; U.S. Pat. No. 4,181,002 to Eckold entitled "Tools for bending sheet metal"; U.S. Pat. No. 4,434,644 to Gargrave entitled "Rotary bending and forming devices"; U.S. Pat. No. 4,520,646 to Pauzin entitled "Sheet-metal bending brake"; U.S. Pat. No. 4,535,619 to Gargrave entitled "Rotary bending, particularly for press brakes"; U.S. Pat. No. 5,341,669 to Katz entitled "Rotary bending tool with continuous lubrication"; U.S. Pat. No. 5,361,620 to Meadows entitled "Method and apparatus for hemming sheets of metal material"; and U.S. Pat. No. 5,640,873 to Costabile entitled "Punch and die assembly".
However, despite the variety of designs and improvements in the rotary bender art, the industry has not yet developed a long length rotary bender suitable for high production metal stamping dies, dies to form high strength or thick steel and forming long panels in automated machines.
A rotary bending and forming device essentially comprises an operating head and a holder, generally referred to as rocker and saddle, respectively. The rocker is a generally cylindrically formed rocker element having an approximately "V" shaped recess continuous in length with its outer peripheral surface, the angle between the two arms of the V-shaped recess being determined largely by the bend angle of the formed component to be bent, in most cases being on the order of magnitude of 90.degree..
The holder comprises a saddle and generally also a gib. The saddle comprises a saddle block with an approximately semicircular recess, preferably having a smooth precision surface. Such a precision bearing surface ideally provides a low coefficient of friction seat for the rocker element, in an arrangement which substantially increases the load accommodating and long production life capability of the saddle as well as the mating rocker.
Once the rocker element is seated, the gib is releasably connected to the saddle to have a limited portion thereof overlie and lightly bear against and contain the rocker element to its seat. The construction and arrangement of the gib provides for a balanced and stable mount of the rocker element, which insures the proper orientation of its groove throughout the course of its application in a bending or forming procedure.
The gib and/or the saddle may include means for applying lubricant to the outer peripheral surface portion of the rocker element. These lubricating devices afford an economical means for insuring a smooth and effective function of the rocker element and avoidance of unnecessary wear on the related parts.
The rotary bending head and its V-shaped recess cooperate with a correspondingly shaped bottom die, the bent component to be shaped being formed around the bottom die by the recess in the rotary bending head. In the process, the rotary bending head is first subjected to a translational movement by the descending saddle block in which it is pivotably mounted, a rotational movement being superposed on the translational movement during the actual shaping process. The bearing assembly of the rotary bending head in the saddle block is therefore of the utmost importance, since not only does it transmit the pressing pressure, but it must at the same time permit the rotary bending head to rotate as smoothly as possible.
Obviously, the bearing surfaces of the saddle block and the outer periphery of the rocker must be fitted to each other with close tolerances. Benders can only be made in lengths at which these close tolerances can be achieved in the manufacturing process. To date it has not been possible to form hardened saddles and rockers with sufficient dimensional accuracy to have close tolerances at longer lengths.
That is, while benders for making long length bends are known, these benders will usually produce only a limited volume of bends before failure. One such long length bender is available from Ready Technology of Dayton, Ohio, and has the rocker and saddle made of a 4140/4150 prehardened brake die steel. Brake die steel is a good material; it work hardens over time, and for lower production volumes it is a good choice. Benders can be manufactured of this material in, e.g., 24, 36 or 48 inch lengths or longer. There is, however, a problem in that there is not a sufficient dissimilarity between the brake die steel of the rocker and the steel of the saddle as far as hardness. The bending devices are under high compressive load and can be subject to galling if any foreign matter gets between the rocker and saddle. A good separation in hardness between the two contacting members (rocker and saddle) is necessary in order to eliminate galling. Sometimes even the force that is required in the compressive load of the rockers and saddle when bending thick high strength steel is sufficient by itself to cause galling. Accordingly, this medium production type unit is not suitable for commercial high volume or high strength production requirements.
On the other hand, rotary benders for commercial high volume bending of higher strength or thicker steel are also known, and include those manufactured by Ready Technology. These benders have a full hardened steel rocker made from A2 or A6 steel hardened to Rc 60, and a rocker saddle (saddle block) made of through-hardened tool steel hardened to Rc 48-52. However, due to inability to produce the rocker and saddle without warp, it has only been possible to produce these hardened rotary benders in shorter segmented lengths (e.g., 6 inches). In order to bend a long (e.g., a 48") length for a high production application, a series of benders has to be abutted end to end and aligned. However, this approach is not always practical or successful because (1) the greater the number of segments, the greater the cost and (2) the more segmented the bender, the greater the chance for misalignment of segments and jamming. If one of the saddles has been bumped or knocked out of position and the rocker becomes trapped and impaired from freely rotating, the result is a failure in the bending operation and a damaged part or tool. Due to the expense and time involved in custom manufacturing such units, and due to the labor involved in alignment and monitoring, these units do not represent a commercially significant market.
Bender manufacturers have attempted to manufacture longer high strength bender devices. For example, Ready Technology has worked with gas nitride to case harden brake die steel. The result is a harder and better wear surface. However, the input of heat and friction tends to cause warped, distorted shaped parts. Particularly for extended length benders, it is critical that the fit and alignment of the parts be dead straight and accurate. That is, for the rocker to rotate within the saddle it needs to be extremely true. This requirement for the rocker and saddle to be absolutely true has dictated the limits on the lengths to which rockers could be manufactured.
The present inventors have extensively experimented with the machining process in an effort to develop a longer length full-hardened rocker. It is well known that, to machine a full-hardened rocker, the V-shaped notch should be machined out while the rocker is still soft before the rocker is hardened, since machining when the rocker is hard is cost prohibitive. However, when the V-shaped notch is machined out of the soft steel rocker before sending the rocker to a through-hardening oven, the result is a bowed piece. Apparently, grinding the rocker introduces stresses and residual stresses which cause the rocker to bow rendering it distorted and unusable.
Accordingly, there remains a need for a long length rotary bender for commercial bending of higher strength or thicker steel. There is likewise a need for a method of manufacturing such a long length rotary bender.